1. Technical Field
The invention relates to an apparatus for scanning a rotating information carrier, which information carrier has mutually substantially parallel tracks for the recording of information, which apparatus includes a transducer for scanning the information carrier and generating a position signal which is indicative of the position of a scanning point of the information carrier, which point is scanned by the transducer, means for rotating the information carrier about an axis, and means for moving the scanning point radially with respect to the axis.
The invention further relates to a method for scanning a rotating information carrier.
2. Related Art
Such an apparatus is known from U.S. Pat. No. 5,321,676. The known apparatus has coarse positioning means in the form of a slide carrying the transducer and a motor for driving the slide and has fine positioning means for positioning the scanning point with respect to the transducer. The apparatus is suitable for reading information carriers having tracks which together form a spiral. In the known apparatus the scanning means cause the scanning point to follow the track. For this purpose, the position of the fine positioning means is corrected continually. As soon as a signal indicative of the position of the fine positioning means exceeds a threshold value the transducer is moved stepwise. When a command is given to read and/or write a file the starting point of the file generally does not have the same tangential position as the scanning spot. It takes some time, hereinafter referred to as rotational latency time, until the rotational position of the starting point and that of the scanning point coincide. However, during reading and/or writing it is desired to have a minimal rotational latency time.
It is an object of the invention to provide an apparatus and a method which enable the rotational latency time to be reduced.
To this end, the apparatus in accordance with the invention is characterized in that the apparatus has a scanning mode in which during reading and/or writing of a continuous file the scanning point is moved both from one track to another track in a first radial direction and from one track to another track in a second radial direction opposite thereto.
In the method in accordance with the invention, for scanning a rotating information carrier, which information carrier has mutually substantially parallel tracks for the recording of information, a signal is generated which is indicative of the position of a scanning point of the information carrier, the information carrier being rotated about an axis and the scanning point being moved in a direction transverse to the axis, which method comprises a scanning mode in which during reading and/or writing of a continuous file the scanning point is moved both from one track to another track in a first radial direction and from one track to another track in a second radial direction opposite thereto.
In the apparatus and the method in accordance with the invention reading and/or writing of file information is started at the tangential position of the information carrier which instantaneously coincides with the tangential position of the scanning point immediately upon reception of the command in said scanning mode. Consequently, there is no rotational latency time. However, there may be a latency time during reading and/or writing of the file. As a rule, it is favorable to effect reading in accordance with said scanning mode if the information carrier should traverse a comparatively large angle before the tangential position of the starting point of the file has come within the range of the scanning point.
It is to be noted that from U.S. Pat. No. 5,570, a method is known for reducing the average rotational latency time. In this method the access time is calculated for different files. The information carrier is then divided into tangential zones. Within each of said zones an area is determined that can be reached within the time interval required for the rotation of the relevant tangential zone to the transducer. Subsequently, the command having the smallest rotational latency time is selected from queue of commands. This latency time is the sum of the times required for a radial and a tangential excursion. The known method is only suitable for the situation that there are different search commands. However, it is also desirable to minimize the time required for reading in the case that there is only one search command.
Moreover, it is to be noted that from U.S. Pat. No. 5,283,875 a method is know in which blocks of information are recorded in reverse order on the information carrier. Thus, it achieved that the operating system already reads in blocks having a higher block number during the rotational latency time. However, this method does not provide a solution in the case that a track has been inscribed only partly. Said method does not lead to a reduction of the rotational latency time when applied to information carriers written in a customary manner.
A variant of the method in accordance with the invention is characterized in that in said scanning mode the scanning point moves one time in the first radial direction and subsequently moves more gradually in the second radial direction. This variant has the advantage that not many abrupt movements of the scanning point are required, which contributes to a low power consumption.
Another variant of the method in accordance with the invention is characterized in that during every revolution the scanning point jumps from one track to another track in the first radial direction and jumps from one track to another track in the second radial direction. This variant enables information streams such as video/audio streams to be made available rapidly.
An apparatus in accordance with the invention can choose from the various methods in accordance with the invention to scan the information carrier or can scan the information carrier in a conventional manner, i.e. sequentially. The choice from the different variants of the method in accordance with the invention and the conventional method may depend, for example, on the type of file, the type of information carrier (spiral/circular tracks), the instantaneous position of the information carrier relative to the transducer, and the permissible power consumption during the displacement of the transducer. The information carrier may be scanned for example in a conventional manner if the starting position of the file nearly coincides with the range of the transducer. In this situation there is no rotational latency time when the conventional method is used.
There are several possibilities of storing information on an information carrier. The information may be stored, for example, as a magnetically or an optically detectable pattern. The tracks may be separate and concentric with respect to one another but alternatively they may together form a spiral. The method is particularly suitable for an information carrier as proposed in the format-C DVD-RAM, in which the tracks are divided into sectors having a header, sectors of mutually adjacent tracks having mutually the same tangential boundaries. Since mutually adjacent sectors have the same tangential boundaries the transducer can directly read a following sector upon a radial displacement at the end of a sector.
The file to be read or written is for example a data file, an audio file or a video file or it includes information referring to other files.
In an attractive embodiment the apparatus has a buffer coupled to the transducer. This allows information of a file read from the information carrier in said scanning mode to be made available in a sequential order and/or information which is available in a sequential order to be arranged in the order in which it is written onto the information carrier. A favorable embodiment of the apparatus in accordance with the invention is characterized in that the means for moving the scanning point radially with respect to the axis include coarse positioning means and fine positioning means, jumping to an adjacent track being effected by the fine positioning means. This allows jumps to be made rapidly using little power.